Abrasive boron nitride particles containing phosphorus

ABSTRACT

A tough cubic boron nitride crystal having greater-than-usual impact resistance is prepared by effecting the catalytic transformation of soft hexagonal boron nitride into cubic boron nitride in the presence of sufficient phosphorus or phosphoruscontaining compound to substantially saturate the abrasive crystal with about 0.042 percent by weight of phosphorus.

O United States Patent 1 [111 3,881,890

Birle May 6, 1975 ABRASIVE BORON NITRIDE PARTICLES 3,036,907 5/1962 Bibbins.... 51 309 CONTAINING PHOSPHORUS 3,150,929 9/1964 Wentorf... 51/307 3,192,015 6/1965 Wentorf 51/307 [75] Inventor: John David B a ay. Ohio 3,233,988 2/1966 51/307 [73] Assignee: General Electric Company,

Columbus Ohm Primary Examiner--Donald J. Arnold [22] Filed: Apr. 20, 1973 [2]] Appl. No.: 352,884

[57] ABSTRACT [52] U.S. Cl. 51/307; 51/298; 51/308; A tough cubic boron nitride crystal having greatep 51/309; 117/100 B than-usual impact resistance is prepared by effecting [51] ll lt. Cl 824d 3/14; 824d 3/28 the catalytic transformation of soft hexagonal boron [58] new of Search 423/284' 51/307 nitride into cubic boron nitride in the presence of suf- 51/308, 309, 298; 106/55, 395; 117/100 ficient phosphorus or phosphorus-containing compound to substantially saturate the abrasive crystal [56] Refennus cued with about 0.042 percent by weight of phosphorus.

UNITED STATES PATENTS 2,947,617 8/1960 Wentorl' 51/307 8 Claims, N0 Drawings ABRASIVE BORON NITRIDE PARTICLES CONTAINING PHOSPI-IORUS BACKGROUND OF THE INVENTION Boron nitride is known in a soft form and in two hard forms. The soft form is a hexagonal crystal which is analagous to graphite and is useful as a lubricant. In the hard form, particles of the material possess a hardness aproaching that of diamond. Grinding wheels utilizing abrasive boron nitride are superior to grinding wheels using diamond particles or other abrasives when used to grind hard tool steels.

Neither of the hard abrasive types of boron nitride has been found in nature. The transformation of the soft hexagonal form into a hard form having a cubic crystalline configuration corresponding to the atomic crystal configuration of zincblende was disclosed in Wentorf US. Pat. No. 2,947,617. The transformation of the soft form of boron nitride to a hard hexagonal crystalline form having an atomic crystal structure corresponding to wurtzite was disclosed in Bundy et al. US. Pat. No. 3,212,851 The present invention applies only to cubic boron nitride of the zincblende structure prepared by catalytic transfonnation from the soft form of hexagonal boron nitride.

Wentorf's catalytic transformation used as catalyst materials alkaline metals, alkaline earth metals, lead, antimony, tin, and nitrides of all of these metals. The presence of one or more of these catalyst materials enables the transformation to take place in the cubic boron nitride stable region of the phase diagram at a point near the equilibrium line of such diagram.

During the production of cubic boron nitride a small quantity of catalyst material is trapped in the crystal structure. The residual quantity of catalyst material present in the crystal structure may be augmented by other materials present during the transformation. For example, graphite or carbon black may be added to the charge to provide cubic boron nitride crystals containing carbon paticles. Such particles enhance the abrasive quality of the final crystal. Other additives or dopants may be included in the intital charge to produce a final abrasive particle containing such additives or dopants. The use of beryllium as a dopant to make cubic boron nitride electrically conducting is disclosed in Wentorf US. Pat. No. 3,078,232. The use of silicon and germanium for this purpose is disclosed in Wentorf US. Pat. No. 3, 1 4l ,802. The use of selenium and sulfur is disclosed in Wentrof US. Pat. No. 3,216,942.

SUMMARY OF THE INVENTION ln accordance with the present invention it has been discovered that cubic boron nitride crystals in which phosphorus is incorporated are not only very tough but also very regular crystals. When such crystals are incorporated as abrasive particles in vitreous-bond, metal bond, or resin-bond grinding wheels they give improved results in the grinding of hard tool steels.

DESCRIPTION OF THE PREFERRED EMBODIMENT Two criteria for determining the usefulness of various cubic boron nitrides are (l) the particle size distribution produced by the formulation, and (2) the friability index. In determining the friability index, crystals of a given mesh size are subjected to repeated impact and the loss in size of the crystals due to fracture is then measured. Half-gram samples are used for this purpose. The friability index is the percentage of loss to the new smaller standard mesh size. Thus, the higher the friability index the weaker the crystal. Accordingly, it is desirable that the process used produce not only a crystal of low friability index but also crystals in the size ranges which are in greatest demand commerically.

When cubic boron nitride crystals are saturated with phosphorus, phosphorus is present to about 0.042 weight percent in the crystal. While lower proportions of phosphorus produce improved crystals the preferred form of practicing the invention is with phosphorus present at about the saturation point. Of course, a much higher percentage of phosphorus than 0.042 weight percent must be present in the initial charge in order to have a final product which is saturated with phosphorus. Preferably, the initial charge contains 0.5 to 7.0 weight percent phosphorus. In the practice of the invention the initial charge is subject to temperatures and pressures in the cubic-stable region of the cubichexagonal phase diagram for a period of 2 to 20 minutes and preferably for a period of 6 to 15 minutes.

Following usual procedure the phosphoruscontaining charge is placed in the reaction chamber of a high-pressure high-temperature apparatus. The temperature is then raised to at least l,200C and the pressure to a level where cubic boron nitride is stable at the particular temperature to which the charge is subjected. This is usually a pressure in excess of 40 kilobars. The temperature is then allowed to fall by cutting off the heating circuit and then the pressure is reduced. The charge is then withdrawn from the apparatus and the cubic boron nitride particles separated from the charge matrix.

Not all phosphorus-containing formulations yield the same results. Many formulations give such a small yeild of cubic boron nitride as to make them usable commerically. The following examples 1 through 28 give the results of various phosphorus-containing formulations:

Composition Description l 40 Mesh Friabili Example No. (Weight Percentages) of Crystals In Yield of lZO K Iesh 1 83.5% BN, l0% Li N, 3% LiH, Yellow 33 50 3% LiOH, .5% P N,

2 83% EN, 10% Li N, 3% Lil-I. Yellow 35 33 3% LiOH, l.0% P N 3 82% BN, l0% U N. 3% Lil-l, Yellow 43 26 3% LiOH, 2.0% P;N

4 83% BN, 10% Li N, 3% LiH, Yellow SI 36 3% LiOl-l, 1.0% P

S 82% BN, 10% Li N, 3% UPI, Yellow 46 27 3% LiOH, 2.0%?

C onlinued Composition Description 80/140 Mesh Friability Example No. (Weight Percentages) of Crystals ln Yield of 100/120 Mesh 6 81% EN, 10% 1.1,N, 3% 1.111, Yellow 44 26 7 85% EN, 10% Li N, 2% Nl-hcl, Yellow,

2% NH,l-|,P0,, 1% P,N,, Very Small 8 85% BN, 10% 1.1,N, 3% Nl-l,C1, Yellow,

1.5% NH,l-1,P0,, 0.5% 15M, ver Small 9 83.5% BM, 10% Li N, Yellow 46 30 4% NH.C1, 1.0% NHJ-LPO. 1.5% P,N,

10 84% BN, 10% 1.1,N, Yellow 4% Nl-LCI, 1.0% NH4H,PO4, Very Small 1.0% P,N,,

1 84% BN, 10% Li N, 2% Nl-LCl, Yellow 2% NH,H,PO,, 2% P Very Small 12 80% EN, 10% L1,N, 3% LiH Yellow 46 2s 3% 1.1011, 2% P, 2% l 1l-1,l-l,P0

13 80% BN, 10% 1.1,N, 3% 1.111, Black and 50 31 3% LiOl-l, 2% P, 2% (NI-LLCO, Yellow 14 86% EN, 10% Li N, 2% P, Black and 2% (Ni-l ),CO Yellow 15 80% EN, 10% L1,N, 3% 1.111, Yellow 42 31 3% LiOH, 2% Nl-LBB, 2% P 16 80% EN. 10% 1.1,N, 3% 1.111, Yellow 3% 1.1011, 2% P, 2% (15111,),50 Very Small 17 80% BN, 10% L1,N, 3% LiH, Light Yellow 50 29 3% LiOH, 2% P, 2% NH4F 18 83.5% BN, 10% Li,N, 3% L111, Yellow 47 48 19 83% EN, Li,N, 3% 1.111, Light Yellow 50 34 3% LiOl-l, 1.0% P10,

20 82% BN, 10% 1.1 181, 3% L1H, Light Yellow 53 34 21 81% EN. 10% um, 3% L111 Light Yellow,

3% Li011, 3% no, Small 22 78% EN, 10% Li N, 3% L111 Light Yellow,

3% L10H, 6% P 0 Small 23 82% BN, 10% 1.1,N, 3% L111, Black 30 41.8

3% 1.1011, 2% BP (120/140) 24 80% EN, 10% L1,N, 3% 1.111, Yellow 47 26 3% H011, 2% P, 2% NlLCl 25 79% EN, 10% Li;,N, 3% 1.111, Yellow 49 34 3% 1.1011, 2% P, 3% Nl-LCI 26 78% EN, 10% 1.1,N, 3% L1H, Yellow 30 27 3% U011, 2% P, 4% NH Cl 27 79% EN, 10% Li -,N, 3% L111, Yellow 36 38 3% LiOH, 1% NH HgPO41 4% Nl-LCI 28 81% EN, 10% Li N, 3% 1.111, Yellow 24 4 3% LiOH, 3% NlLCl (/120) 'CP. Red Phosphorus Example 24 was the best formulation as it gave a -Continued good yield of the desirable 80/ 140 material and had a Friabifily friability index of 26 for the /120 material. In this 60 Mesh Size sh Index example, lithium nitride was the catalyst and ammo- 80/100 16.7 30.2 nium chloride functioned as a mineralizer. {38;}28 1 :2 3: The particle size distribution and frlablllty of the ma- /170 14.6 13. 21 terial from Example 24 were as follows: /200 200/230 2.8 i i y 65 230/270 42 Mesh Size Weight Index 270 325 3 0 325/400 0.7 +60 2.1 400 0.2 60/80 15.9 35.8

i 6 Phosphorus doping produces an extremely tough cubic fl'labllity index dogs not mean that it Qannol give p boron nitride crystal having nearly perfect crystallinity. rior performance m certam appllcatlons- Parameters When such crystals were used as the abrasive particles Such as the yp of mild used, the P of abrasive in resin-bond wheels considerably improved results in the bond, the wheel speed, the wheel infeed, the were achieved in certain comparison grinding tests. 5 table speed, the type of coolant, if any, used, and others The following Table 1 compares dry grinding test reenter into the performance equation. All of these tosults in resin-bond wheels using nickel-coated cubic gether with the properties of the material to be ground boron nitride as the abrasive on T-l5 steel. In the conmust be taken into consideration in order to obtain optrol (cubic boron nitride) wheels the cubic boron nitimum effectiveness in wheel performance.

tride contained about 1.0% by weight of carbon, an ad- 10 While the invention has been described with referditive which considerably increases the toughness of ence to certain specific embodiments, it is obvious that the crystal. The wheels containing phosphours-doped there may be variations. Accordingly, the invention cubic boron nitride used crystals which were saturated should be limited in scope only as may be necessitated with phosphorus but contained no carbon. is by the scope of the appended claims.

TABLE I GRINDING RATIOS IN DRY GRINDING OF T-lS STEEL lnfeed (Inches) T-l 5 steel is an iron-base steel containing 12 weight What I claim as new and desired to secure by Letters percent tungsten, 5 weight percent vandium 4 weight Patent of the United States is:

percent chromium and 5 weight percent cobalt, and l. Abrasive cubic boron nitride particles substantially was hardended to R 58-60. saturated with about 0.042 weight percent of phospho- The following Table III compares dry grinding test rus.

results in resin-bond wheels using nickel-coated cubic 2, A br ive wheel in which the matrix contains boron tr a the abrasive Steel cubic boron nitride particles as claimed in claim 1.

TABLE II GRINDING RATIOS IN DRY GRINDING 0F M-2 STEEL Infecd (Inches) Nickel-Coated Abrasive Mesh Size .(JOI .002 .003 .004

Cubic boron nitride 100/ I20 233 I6 10 Phosphorus-doped cubic boron nitride I00/ I 20 329 46 l 9 9 Cubic boron nitride 30/030 199 S4 34 I7 Phosphorus-doped cubic boron nitride 80/ I00 422 74 SI 19 50 M-2 steel is an iron-base steel cont inin bo 4 3. An abrasive wheel as claimed in claim 2 in which weight percent chromium, 2 weight percent vanadium, the matrix 15 a resin matrix- 6 weight percent tungsten, and 5 weight percent molybdenum, and was hardened to R -62.

It is here emphasized that the properties of abrasive particles which make them superior for some grinding 5. An abrasive wheel as claimed in claim 2 in which applications make them inferior for others. For examthe matrix is a vitreous matrix. ple, insome wet grinding applications resin bond wheeis containing phosphorus-doped abrasive particles were 60 inferior in grinding ratio to similar wheels in which the 4. An abrasive wheel as claimed in claim 3 in which 55 the abrasive particles are nickel-coated.

6. An abrasive wheel as claimed in claim 2 in which the matrix is a metal matrix.

abrasive particles did not contain phosphorus. It ap- 7. The method of catalytically preparing boron nipears that a low friability index is not in all cases a detride particles with substantially phosphorus-saturated sirable property. Low friability and regularity of crystal cubic crystalline structure which comprises mixing soft structure go together. In some grinding applications the hexagonal boron nitride with 0.5 to 7 weight percent of weaker crystals which can be more easily cleaved to ex- 3 m mber selected from the group consisting of phospose a fresh cutting surface perform more effectively. phorus, a phosphorus compound, and mixtures thereof,

Thus, the mere fact that a particular crystal has a high subjecting the resulting mixtures to an elevated tempersists by weight of about soft hexagonal boron nitride, 10% lithium nitride, 3% lithium hydride, 3% lithium hydroxide, 2% phosphorus and 2% ammonium chloride. 

1. ABRASIVE CUBIC BORON NITRIDE PARTICLES SUBSTANTIALLY SATURATED WITH ABOUT 0.042 WEIGHT PERCENT OF PHOSPHORUS.
 2. An abrasive wheel in which the matrix contains cubic boron nitride particles as claimed in claim
 1. 3. An abrasive wheel as claimed in claim 2 in which the matrix is a resin matrix.
 4. An abrasive wheel as claimed in claim 3 in which the abrasive particles are nickel-coated.
 5. An abrasive wheel as claimed in claim 2 in which the matrix is a vitreous matrix.
 6. An abrasive wheel as claimed in claim 2 in which the matrix is a metal matrix.
 7. The method of catalytically preparing boron nitride particles with substantially phosphorus-saturated cubic crystalline structure which comprises mixing soft hexagonal boron nitride with 0.5 to 7 weight percent of a member selected from the group consisting of phosphorus, a phosphorus compound, and mixtures thereof, subjecting the resulting mixtures to an elevated temperature of at least 1,200*C. and pressure conditions in excess of 40 kilobars, conditions under which the cubic crystalline boron nitride structure is stable, and sequentially reducing the temperature and lowering thE pressure of said mixture.
 8. The method of claim 7 wherein the mixture consists by weight of about 80% soft hexagonal boron nitride, 10% lithium nitride, 3% lithium hydride, 3% lithium hydroxide, 2% phosphorus and 2% ammonium chloride. 